From the Alberta Guide to Education:
Alberta High School Diploma (100 Credits)
Courses in the diploma program as designed for most students who are planning to work immediately after high school or progress into post-secondary study. Courses in the diploma program will end in -1, -2, or -3 depending on the specific stream students require for their post-secondary plans.
Alberta Certificate of High School Achievement (80 Credits)
Also known as the Knowledge and Employability program, courses are designed for students who demonstrate reading, writing, mathematical and/or other levels of achievement two to three grade levels below their age appropriate grade. Courses in the certificate program will end in -4 to align with the diploma program.